Paper 23006 2nd revised version 2012 (4)

Field Experiences in Corrosion Diagnosis and Remediation Solutions for the Bridge Infrastructure of México

Rafael Soto-Espitia Centro de Investigación en Ingeniería y Ciencias Aplicadas – UAEM, Ave Universidad 1001, Cuernavaca, Morelos, México. 62210 espitia78@hotmail.com José Roberto Vázquez González Caminos y Puentes Federales de Ingresos y Servicios Conexos, Calzada de los Reyes 24, Cuernavaca, Morelos, México. 62130 Salvador Ascencio Centro de Innovación en Integridad de Infraestructura y Ductos, Rio Nazas 6, Cuernavaca, Morelos, México. 6290l

Instituto de Ciencias Físicas, UNAM, Ave Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos, México. 62210 Edgar Maya Centro de Innovación en Integridad de Infraestructura y Ductos, Rio Nazas 6, Cuernavaca, Morelos, México. 6290l Jorge I. Canto Corrosión y Protección Ingeniería S.C., Rio Nazas 6, Cuernavaca, Morelos, México.

6290l

Lorenzo Martínez de La Escalera Corrosión y Protección Ingeniería S.C., Rio Nazas 6, Cuernavaca, Morelos, México.

6290l Lorenzo Martínez-Gómez ABSTRACT The research initiative to be described relates to the concern of the current Mexican transportation agencies about infrastructure integrity particularly in the sector of highway bridges. We report analytical and field work on corrosion diagnosis, solution development, and monitoring of a set of bridges representative of past and emerging construction technologies under the scope of corrosion engineering in tropical environments. We consider three reinforced concrete bridges, two of which are cable-stayed systems. Diagnostic procedures were applied on piles as well as other structural components involving field visual inspections as well as concrete resistivity, impact strength, and reinforcing steel–concrete electrolyte half cell potentials. Age and sea coast proximity were two important factors affecting the reinforced concrete integrity. The oldest bridge over seawater exhibited a significant need for attention and repair. A CP (cathodic protection) system was installed including a remote monitoring

system to survey rebar concrete potential performance and to show the effectiveness of the CP solution. In the diagnosis, a cable stayed bridge near the coast of the Gulf of Mexico exhibited some deleterious effects of corrosion of reinforcing bars in the visual inspection as well as the half cell potentials, concrete resistivity, and impact strength.

Keywords: Infrastructure, bridges, corrosion, concrete, steel, cathodic protection INTRODUCTION The corrosion of steel reinforcement in concrete is one of the most significant problems in preserving the structural integrity of civil structures such as bridges, tunnels, marine docks, airports, foundations, and other infrastructure. The Hoar report estimated that corrosion losses in the building industry sector in the United Kingdom reached £250 million per year. 1 In 1985, NACE (The National Association of Corrosion Engineers) reported that in the United States there were 300,000 bridges requiring CP. The protection of this valuable segment of US infrastructure along with related repair work was estimated to cost around $23.1 billion.2-9 Steel components in structures exposed to air, soil, and water corrode from the first day in the field. The life in service of structures primarily depends on the ability to control the rate of corrosion of the structure in a given environment. Normally, the rate of corrosion of steel depends on the availability of water and oxygen in the surrounding electrolytes. However in acidic environments, corrosion can proceed even in the absence of oxygen and water.

Concrete usually provides an alkaline environment to the reinforcing bars, where in principle corrosion should not evolve rapidly. If the alkalinity of concrete is relatively high a passive oxide layer usually develops on the surface of the reinforcing steel bars. The low electrical conductivity of concrete is also a factor preventing corrosion. Chlorides, carbonates, and other pollutants either in an air environment or in soil and water when submerged tend to penetrate concrete structures and to significantly change both pH and concrete electrical resistivity. The pH may drop from the expected values of 12–14 to as low as 7 or 6, and resistivity may be reduced from the usual value of 8,000–10,000 Ω-cm to much lower values. Both pH and resistivity when diminished can create a very corrosive environment for the rebar steel. The likelihood of corrosion of rebars in concrete is usually diagnosed by the steel rebar to concrete half cell potential. The actual corrosion damage to concrete structures may be made evident by cracking on the surface and assessed by measuring the loss of mechanical integrity with either sounding or impact testing.

Regulations relative to the control of corrosion and integrity management of reinforced concrete structures are relatively scarce in many countries. This contrasts with the rules for pipelines transporting oil, gas, and hazardous fluids, where stiff regulations for corrosion

control exist within the US, where they are put in place by the DOT (Department of Transportation), and in most countries in the world. In fact the US DOT Office of Pipeline Safety is very specific in enforcing coatings and cathodic protection and internal corrosion control. The Code of Federal Regulations further stipulates that the corrosion protection systems should be subject to frequent monitoring to ensure that corrosion will not cause leaks and explosions.

The highway infrastructure in Mexico is expanding and evolving rapidly; however medium and old aged constructions still represent a significant percentage of the assets for the overall mobility of the country. Calls for attention to the need for corrosion control of rebar steels and steel in general have occurred due to the collapse of bridges or costly investments in urgent repairs. This work presents the efforts, sponsored by the country’s official research and development agency together with highway authorities, addressing the state of reinforced concrete components of three main bridges representative of the ones existing in Mexico: old, medium aged, and recent. The construction of cable-stayed bridges in Mexico is emerging; actually there are more of 10 bridges of this type and now one of the largest cable-stayed bridges of the Americas is in construction. The Baluarte Bridge is located in the Sierra Madre in the states of Durango and Sinaloa with a total length over 500 m and height of up to about 400 m.

This study considers the Mezcala Bridge, currently the second longest and tallest in Mexico.

This bridge is of utmost importance since it is part of the Del Sol highway that runs from Mexico City to Acapulco and is crucial for communications between central Mexico and the Gulf of Mexico and the southern Pacific regions. In 2008 the AADT (Annual Average Daily Traffic) was 22,416,507 vehicles. The total construction cost was $64 million and its construction was carried out in 24 months, finishing in 1993. The bridge is located at a distance of approximately 135 km (83.89 mi) from the coast of the Pacific Ocean.

The second bridge to be considered in this paper is the Dovali Jaime Bridge located at the core of, servicing freight and passengers from central and northern Mexico throughout the southeast of the country along the coast of the Gulf of Mexico. It was the first cable-stayed bridge built in Mexico. The bridge is located approximately 20 km (12.43 mi) from the coast of the Gulf of Mexico and it is a vital part of the communications infrastructure in one of the most prosperous areas of the country's oil and petrochemical industry.

Our third unit of analysis is a plain concrete bridge built over piles crossing the marine waters of the Gulf of MĂŠxico at the interface with the Laguna de Terminos, the largest body of brackish water in the country. La Unidad Bridge was built in 1982, in Isla Aguada, Campeche State in the Southwest of Mexico. At 3277 m (2.04 mi) long, La Unidad Bridge is the second longest bridge of its kind in Mexico. This bridge was important for many years because it serviced traffic from the whole of northern and central Mexico to the southeast and the Yucatan

Peninsula. Although other routes were opened in the last years, the crossing at Isla Aguada is still of utmost importance. Corrosion damages became apparent after just a few years of service, and have been subject to many repairs and studies.

Figure 1: Aerial view of the bridges: a) Mezcala in central-south Mexico, b) Dovali Jaime at the core of the petrochemical industry, c) La Unidad at the joining of the Gulf of México and Laguna de Terminos.

Mezcala Bridge is located at Km 219+000 of the Mexico–Acapulco highway (Figure 1a). It has a total length of 882 m (964.57 yd), with spans of 80 m (87.49 yd), 311 m (340.11 yd), 300 m (328.08 yd), 84 m (91.86 yd), 68 m (74.37 yd) and 39 m (42.65 yd). It has a continuous steel deck 882 m (964.57 yd) long with a cross section 18.10 m (59.38 ft) wide, three main reinforced concrete piles with maximum dimensions of 11 × 21 m (39.09 × 69.9 ft) and variable wall thickness, and two secondary piles with a maximum height of 169 m (214.35 yd). The superstructure is supported by 140 braces, the longest being 185 m (202.32 yd) long, arranged on three reinforced concrete pylons, forming a portal frame H, the tallest having a height of 73 m (79.83 yd). The foundations, with dimensions in plan of 19 × 29 m (62.34 × 95.14 ft) thickness, are important as a consequence of the degree of seismic activity in the zone. It was constructed from sections of 3 m (9.84 ft) high with towers and cranes using slip form. The superstructure, with a length of 400 m (437.45 yd), was assembled on the banks and erected by hydraulic jacks.

Dovali Jaime Bridge is located at Km 16+470 of the highway Nuevo Teapa–Cosoleacaque.

With respect to the superstructure, it is formed of a main span of 698 m (763.34 yd) of cablestayed and two viaducts, 240 m (262.42 yd), and 232 m (253.72 yd), respectively, adding up to a total length of 1170 m (1279.53 yd) (Figure 1b). The viaducts have spans of 48 m (52.49 yd), 50 m (54.68 yd), and 60 m (65.63 yd) while the main sections have spans of 30 m (32.81 yd), 50 m (54.68 yd), 60 m (65.63 yd), 112 m (122.48 yd), and 228 m (249.34 yd). It is worth mentioning that the bridge has two joints, the first between supports 7 and 8 and the second between supports 11 and 12.

La Unidad Bridge has 1512 piles, 549 beams, 108 stages of reinforced concrete, and a cross section of 10 m (32.81 ft) and is approximately 7.0 m (22.97ft) above sea level.

Figure 2: General view of the bridges: a) La Unidad conventional structure of reinforced concrete and piles, b) The first Mexican stayed-cable, named Dovali Jaime, c) The stayed-cable of Mezcala in Central Mexico.

The types of failures that occur at bridges in service are due to four main factors: fundamental problems of design, constituent materials issues, construction procedures, and operation under live loads. The types of failures may originate from defective construction materials

where cracks can spread or grow or because of loads that the structure is subjected to at any given time, which can lead to collapse. There are also failures that have their origin in the building process, usually related to defective or limited quality control procedures and therefore lack of compliance with the specifications of the work. The failures due to operation are normally associated with overloading because the live charges are greater than expected.

Design charges may be exceeded due to increases in traffic flow, higher than predicted wind speeds, earthquakes of high intensity, and of course possible combinations of these factors.

Previous works in the field of corrosion assessment in concrete structures describe in detail the methodology used in the present study for evaluating and diagnosing each of the bridges considered.9-11. The first step was a detailed visual inspection of the structural components of the bridges. A next step was locating within the structures the steel reinforcements to be tested and assessed. The measurements involved finding delamination damage by sounding and assessing the delaminated areas using a spring-driven hammer. The study also involved electric continuity verification of steel reinforcement, concrete resistivity measurements, and measurement of concrete carbonation and electrochemical half cell steel to electrolyte potentials in selected areas.

Detailed visual inspection Visual inspection of the bridge started with the completion of a data sheet on the structure’s history and its surrounding environment, identification of any damage to each element, and the creation of a photo record of site visits. The visual inspection produces a first appraisal of the physical condition of the structure.12 Detection of hidden corrosion defects by sounding Initially, the effects of the damage by corrosion in steel may not be seen at a glance, since the delamination happens internally and does not manifest on the exterior surface of the structure.

When a delamination exists, the space between the solid and loose concrete produces a particular sound that allows identification of the affected area. This acoustic inspection technique was applied using impact on the surface of the concrete. 13 Electric continuity verification of steel reinforcement Electrical continuity within the reinforcing steel grid is required for the selection and application of future corrosion mitigation methods. Electrical continuity is determined by exposing the reinforcing steel at several locations and testing it using a high impedance multi-meter.

Electrical continuity is also checked at the locations where there is exposed steel. As per Section 4.3.1.6a of the ACI 222R-01 Standard, if the potential difference between the reinforcing bars is less than one millivolt, then the reinforcing steel is deemed electrically continuous.

Electrical resistivity evaluation of the concrete Healthy concrete usually has high resistivity in the range of 12,000 立-cm. The resistivity is a measurement of the ability of the concrete to inhibit the passage of ions and is therefore an estimate of how protective the concrete is to the embedded steel. In the case of concretes which have low resistivity due to carbonation or chloride penetration, the ion transfer through the specific media is easier and a higher likelihood of corrosion exists. The sample zones of concrete are tested in wet and dry conditions. Additionally, testing of concrete resistivity provides useful information that can be used for cathodic protection design and provides understanding as to whether the system chosen for rehabilitation is compatible with the existing concrete. For example, concrete with less than 150 立-m resistivity is ideal for galvanic protection of reinforcing steel. The electrical resistivity is a material property and corresponds to the reciprocal of its conductivity; the unit of measure is 立-m. Resistivity depends largely on the degree of saturation of the pores of the concrete, and to a lesser degree on the hydration of the paste and the presence of salts dissolved in the aqueous phase. It is based on variables such as cement type, inorganic additives, the water/cement ratio, and the porosity of the structure, among others. Since the resistivity is one of the factors that control the rate of steel corrosion in concrete, there is increased interest in determining this intrinsic property of the concrete.14 Corrosion potential measurements The rebar to electrolyte corrosion potential readings of the steel reinforcement were taken using copper/copper sulfate (Cu/CuSO4) reference electrodes (CSE). These measurements were used to locate areas of likely corrosion activity, establishing the potential shift area through a complete potential mapping. A 1.20 m spaced grid was traced on the surface of the concrete.15 The reference electrode and the steel of the exposed reinforcement were connected, and a plane of the surface of each element was drawn, indicating the potential values of each node on the grid. Isopotential lines were drawn to generate maps of the likelihood of corrosion.

Sampling of concrete cores Core extraction is completed using a wet coring machine with a diamond core barrel. Special care is taken in the management of samples to avoid contamination as per the ASTM C42 standard.16. The core samples must have a minimum diameter of 0.005 to 0.0075 m, depending on the size of the aggregate, and are cut at different depths. The cores are used for chloride and carbonation testing. They are taken not only in areas where there is deterioration, but also where concrete appears to be in good condition. The use of a rebar locator allows the samples to be taken in close proximity to the reinforcing steel and allows the depth of cover to be measured in order to test its correlation with the actual depth of the steel.

Evaluation of chloride penetration Reinforced concrete in permanent or intermittent contact with sea water may suffer penetration of sulfates and chlorides by osmosis, capillary action, and diffusion. Chlorides initiate corrosion by breaking down the naturally protective oxide layer on the steel. Sulfates damage concrete by producing expansive compounds in the cement paste, which further facilitates the penetration of the chlorides and corrosion of the steel. Any damage facilitates further contamination and the process is accelerated. The chloride ion content can be measured as a percentage by weight of the concrete as per the AASHTO T260 standard. The percentage chloride ion content by weight of concrete is measured using the ‘Revised SHRP Chloride Analysis Procedure’. A chloride ion content below 0.030% by weight of concrete is considered to be below the threshold for chloride induced corrosion of the reinforcing steel. If the chloride levels climb above this threshold, the reinforcing steel may lose its passive layer and could initiate corrosion activity.

Evaluation of concrete carbonation The carbonation of concrete occurs when the pH of the concrete, normally between 12 and 13, diminished to pH values between 9 and 10. When this occurs, the layer of iron oxide or passive layer naturally formed in high pH concrete disappears, thus allowing corrosion to occur more readily. Concrete core samples are broken in half in the laboratory and the freshly exposed concrete is sprayed with a solution of 0.15% phenolphthalein in ethanol. Pink or purple colour of the indicator solution corresponds to a pH of 10 or higher, indicating sufficient alkalinity to maintain the passive oxide layer. When the solution does not change colour it indicates that the sample has a pH of 10 or less, which indicates carbonated concrete.

It should be noted that the field investigations were carried out using systematic, organized, and efficient procedures to minimize the risk of leaving out of the evaluations any relevant components of the bridges.

RESULTS AND DISCUSSION Visual inspections and soundings Images of the visual inspections and soundings on the Mezcala, La Unidad, and Dovali Jaime bridges are shown in Figure 3.

Figure 3: Visual Inspection and detection of hidden corrosion defects by sounding: a) Mezcala Bridge, b) corrosion damage at La Unidad, c) cracking in the columns of Dovali Jaime Bridge.

According to the detailed visual inspections, Mezcala Bridge does not present damage; however Dovali Jaime and La Unidad bridges present cracks, rust stain, spalled concrete cover, steel expose due corrosion damage. The detection of hidden corrosion defects by sounding corroborated the visual inspection. The effects of the damage by corrosion in steel may not be seen at a glance, since the delamination happens internally and does not manifest on the exterior surface of the structure. When a delamination exists, the space between the solid and loose concrete produces a particular sound that allows identification of the affected area. Mezcala sounding evaluation did not reveal any damaged or delaminated areas.

Sounding defects were positive in some components of Dovali Jaime Bridge as well as La Unidad Bridge, as was apparent corrosion-induced cracking of concrete.

Electrical resistivity evaluation of the concrete The resistivity measurements performed on the concrete structures of Mezcala Bridge were on average greater than 20 kΩ-cm, and according to Table 1 these values represent a very low risk of corrosion.

Table 1 Comparison of relationships between concrete resistivity and corrosion risk. 14 Resistivity cm)

(kΩ- Corrosion risk

>20 kΩ-cm

Low corrosion rate

10 to 20 kΩ-cm

Low to moderate corrosion rate

5 to 10 kΩ-cm

High corrosion rate

< 5 kΩ-cm

Very high corrosion rate

According to Table 1values between 10 and 20 kΩ-cm correspond to low risk to moderate corrosion rate. The resistivity measurements obtained at Dovali Jaime Bridge are also acceptable since about 25% ranged between 10 and 20 kΩ-cm. The rest were above 20 kΩcm. In the case of La Unidad Bridge, most of the measurements of the electrical resistivity of concrete were less than 5 kΩ-cm, and relative to Table 1 these values below 5 kΩ-cm correspond to a very high risk of corrosion.

Rebar to electrolyte potential measurements The measurements of CSE half cell rebar electrolyte potentials performed at Mezcala Bridge were all in the range of –15 to –182 mV. According to Table 2, natural potentials more electropositive than –200 mV correspond to low risk of corrosion. Figure 4 shows the potential measurements taken in pile 3.

Table 2 Corrosion potential with respect to the reference electrode Cu/CuSo 15 Corrosion condition (mV)

Corrosion risk

Potentials more positive than - 200 There is a greater than 90% of no reinforcing steel corrosion If you are between - 200 to -350 There is uncertain that there is corrosion

If more negative - 350

You will have a 90% chance that the steel is corroding

Figure 4: Corrosion potential measurements at Mezcala Bridge.

Figure 5 shows the measurements of the rebar electrolyte potentials in structures of the Dovali Jaime Bridge ranging between –10 and –131 mV. A rebar electrolyte potential of –131 mV was measured in the west face. Figure 5 shows the corrosion potential measurements realized in pile 5.

Figure 5: Corrosion potential measurements at Dovali Jaime Bridge.

Figure 6: La Unidad Bridge: a) schematic view of the pile; b) detailed schematic view of zones A and B

Figure 7: Corrosion potential measurements at La Unidad Bridge zone A.

Figure 8: Corrosion potential measurements at La Unidad Bridge zone B.

According to Table 2 the values measured in pile 91 of La Unidad Bridge correspond to high risk of corrosion. Figures 7 and 8 shows the corrosion potential measurements taken in pile 91.

The obtained values of corrosion potential were in the range â&#x20AC;&#x201C;184 to â&#x20AC;&#x201C;577 mV, showing that the highest measurement was in the south face of zone b.

Evaluation of chloride penetration and concrete carbonation In Mezcala Bridge the chloride content were less than 0.030% chloride ions by weight by concrete and carbonation tests showed inappreciable content.

Dovali Jaime Bridge showed chloride content of 0.0590% chloride ions by weight by concrete, according Revised SHRP Chloride Analysis Procedure, the accept range is 0.030 % by weight and carbonation tests showed inappreciable content.

CONCLUSIONS

In Mezcala Bridge, the corrosion potential readings indicated 10% risk of corrosion. The results obtained by the other tests: electrical resistivity, detection of hidden corrosion defects, and detailed visual inspection by sounding, showed no evidence of corrosion. All the results obtained from Mezcala Bridge will serve to set a benchmark for the Mexican bridges located far from the coast and without apparent damage of corrosion.

Corrosion damage of Dovali Jaime and La Unidad bridges are shows in the visual inspection, showing cracks, rust stains, delamination, spalled concrete cover and steel expose. The corrosion potential of Dovali Jaime Bridge readings indicated 10% risk of corrosion and the obtained results of electrical resistivity indicated a possible 90% risk of corrosion in certain areas.

In pile 91 on La Unidad Bridge, the corrosion potential readings showed more than 90% risk of corrosion. The results obtained by other tests for detection of hidden corrosion defects and detailed visual inspection by sounding showed evidence of corrosion. These results were corroborated by electrical resistivity evaluation of the concrete, which showed a very high corrosion rate.

Corrosion monitoring can be a vital part of planned maintenance and life prediction by giving quantitative information about the development of corrosion as aggressive conditions developed in the concrete due to chloride ingress or carbonation. All the techniques applied to these three bridges will be very helpful to know status of the corrosion process and for developed a maintenance plan.

ACKNOWLEDGEMENTS The authors appreciate the support offered by the Caminos y Puentes Federales de Ingresos y Servicios Conexos and its former engineering director, José Guadalupe Tarcisio Rodríguez Martínez, as well as engineer Omar Ortiz Ramirez for the facilities offered for the present study. The authors also thank CIICAP-UAEM and ICF-UNAM. Special thanks go to A. Davila Ramirez and R. Ramirez from Corrosión y Protección Ingenería, S.C., for their technical support.

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